Fluorocarbon solvents, such as trichlorotrifluoroethane, are widely used as degreasing agents due to their excellent solvent power for greases and some emulsion-type lubricants. Trichlorotrifluoroethane also finds wide use in removing solder fluxes from printed circuit boards due to its selective solvency and non-flammability. Since trichlorotrifluoroethane is non-polar, however, it does not remove polar contaminates. Thus, to overcome this inability, trichlorotrifluoroethane has, in the past, been mixed with polar components, such as aliphatic alcohols.
The art has looked towards azeotropic compositions including desired fluorocarbon components, such as trichlorotrifluoroethane, which include the desired polar components, and other components which contribute desired characteristics, such as stabilizers. Azeotropic compositions are desired because they exhibit a minimum boiling point and do not fractionate upon boiling. This is desirable because in vapor degreasing equipment, in which these solvents are employed, redistilled material is generated for final rinse-cleaning. Thus, the vapor degreasing system acts as a still. Unless the solvent composition exhibits a constant boiling point, i.e. is an azeotrope or is azeotrope-like, fractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. This is also important in the use of the solvent compositions to remove solder fluxes from printed circuit boards. Preferential evaporation of the more volatile components of the solvent mixtures, which would be the case if they were not azeotropic or azeotropic-like, would result in mixtures with changed compositions which may have less desirable properties, such as lower solvency for rosin fluxes, less inertness toward the electrical components and increased flammability.
A number of trichlorotrifluoroethane based azeotropic compositions have been discovered which have been tested and in some cases employed as solvents for miscellaneous vapor degreasing applications and for the removal of solder fluxes from printed circuit boards. For example, U.S. Pat. No. 2,999,815 discloses the binary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with acetone; U.S. Pat. No. 3,553,142 discloses the binary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with acetonitrile; U.S. Pat. No. 3,903,009 discloses the ternary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane and ethanol; U.S. Pat. No. 3,573,213 discloses the binary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane; U.S. Pat. No. 3,789,006 discloses the ternary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane and isopropanol; and U.S. Pat. No. 3,728,268 discloses the ternary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with acetone and ethanol.
Unfortunately, as it is recognized in the art, it is not possible to predict the formation of azeotropes and this obviously complicates the search for new azeotropic systems which have application in this field. Nevertheless, there is a constant effort in the art to discover new azeotropic or azeotropic-like systems which have desirable solvency characteristics and particularly a greater versatility of solvency power.
It is accordingly an object of this invention to provide novel azeotropic or azeotropic-like compositions based on 1,1,2-trichloro-1,2,2-trifluoroethane which have good solvency power and other desirable properties for vapor degreasing applications and for the removal of solder fluxes from printed circuit boards.
Other objects and advantages of the invention will be apparent from the following description.